The Flow Of Energy

Dave Rushworth

Through Natural Systems

As managers of natural systems, be it agricultural, commercial or wildlife, it is important to grasp the concept of energy flow. In natural or wildlife systems this will focus mainly on 'Food' or 'Trophic' energy.

Most people will be aware of the scientific principle - 'MATTER can not be created or destroyed (it exists). It changes from one form to another. AT EACH CHANGE from one form to another there IS AN ENERGY LOSS'. We have 'organic' substances which contain Trophic Energy, that have at some stage been 'living'. Examples - coal, (from trees), dead wood and food items of various types. There are also 'inorganic' substances, that have never lived. Examples - rock and associated minerals, iron, salt and other items.

Organic items contain 'food', sometimes only available to bacteria, while Inorganic items contain no food energy. Petrol (gasoline) is derived from oil which originated from plant or animal life (living matter). It contains energy from which edible forms can be manufactured but more usually it is used for the energy that can be released to power mechanical systems.

Put petrol in your fuel tank and your vehicle can move for a certain distance, after which the tank is empty again. The fuel has been converted to movement and a certain amount of heat. Through combustion it is used up and lost through movement and heat and can not be reclaimed. Subjected to extreme heat stones may crack or even melt. They may 'store' heat for a while but they have no energy to produce heat.

Organic substances

Organic substances will burn and produce more heat. Smoke is inefficient combustion - unburned flame - carbon particles. When a log is truly burned up all that remains is inorganic carbon. Because the carbon is devoid of energy, it will not be eaten by any decomposer and lasts almost indefinitely in the environment. Hence the practice of burning the ends of fence poles to prevent them being devoured by termites. When finally broken down by mechanical processes, this carbon may again enter the mineral cycles.

So we have 'matter' that changes from one to another, and 'energy' that flows through and drives the various systems. Imagine a small boy rolling a tyre along a road. For energy input he keeps hitting it with a stick or his hand. As soon as he stops the 'energy input' (originating inevitably from our Sun), the system wobbles and comes to a halt. The same in nature.

Energy input

The Earth's main source of energy is from the Sun. The only natural system for converting the Sun's energy into 'Trophic Energy' (Food) is 'Photosynthesis' using chlorophyll in the (mainly) green leaves of living plants. All life on earth originates from this source. No plants - eventually no physical life ! Plants (with minerals and water) are the only things that produce food and they are thus called PRODUCERS.

Animal species that eat plants are called the first or PRIMARY CONSUMERS (Herbivores). Animals that eat other animals are called SECONDARY CONSUMERS (Predators / Carnivores / Insectivores). Then we have the SCAVENGERS and DECOMPOSERS. After this the remaining Matter goes through the 'car-breakers' - micro-organisms in the soil, that reduce it to its original mineral components. The minerals are then ready to be taken up by plants roots and used to form new plants which repeat the process.

So we have various 'layers' of Consumers on a plant Producer base. Try and visualise these layers diminishing in size to form a 'pyramid' shape - and I will explain why. METABOLISM. 'Metabolism' is the rate at which energy passes through a system or the rate at which an individual uses up energy. Take a 'hypothetical' human as an example - with very simplified calculations.

You have lived for 30 years. You weigh (have a mass of) 100 kilograms. Each day of your life you have put into your mouth 2.5 kg of food (ignore liquids). You have passed out .5 kg of waste matter daily. That leaves a nett intake of 2 kg per day. In our case a year has 300 days. So in each year you have consumed 600 kg of food. In 30 years you have consumed 30 x 600 kgs = 18,000 kgs of food (that went into your mouth and never came out again) - BUT you only weigh 100 kg. At a world 'energy' court you need to explain how you have 'wasted' 18,000 less 100 kgs = 17,900 kgs of valuable food. It has taken 18,000 kgs to produce only 100 kgs. It is not hard to explain.

When we get into a cold bed it warms up from our body heat. We are constantly losing heat (Our head loses about 20% of our body heat). We are (if healthy) constantly moving. We have also grown in size. So 'Food Energy' - as in the case of the motor vehicle - has been lost through 'Heat' and 'Movement'.

People with a 'High Metabolism' will have used up more energy and will be 'thinner' than those who have a 'Low Metabolism' and have used less energy, leaving them 'fatter'. It is easy to understand how an extremely active 'Dwarf Shrew' has a higher metabolism than an Elephant.

The Metabolism of different species in the veld is important in our assessment of 'food' consumption because it means that different species, even with the same biomass, will consume vastly varying amounts of food. With this loss in energy at each 'conversion' it is easy to see that from a large plant (producer) base there will be a much smaller biomass of primary consumers (Buffalo, Kudu and other grazers and browsers).

From a meat base of Herbivores, there will be a much smaller biomass of Carnivores, from which there will be an even smaller biomass of Scavengers and so on, forming the picture of a food or 'Trophic Pyramid'. Each upper layer relies on the 'food base' beneath it. Because of this it is important to remember that, in natural systems, that PREY CONTROLS PREDATOR and not the other way around. In an unrestricted area you will never control Buffalo with Lion or Impala with Leopards. It works the other way around - Prey controls Predator, and the same for all Trophic layers.

Energy flow

Desert areas capture very little food energy. Poor grasslands produce little food. Savannah areas produce more food of greater variety, while forests produce most edible biomass, much of which is not easily available to primary consumers. In hot, wet areas much of the recycling of matter is carried out by decomposers.

Management for productive areas requires that we maintain good plant production and focus much less on animal management. Without the food base we will not have the animals. (A good farmer is a grass farmer - and that is where good grass management comes in.) One needs to assess the metabolism of various species and in their management be aware of the intrinsic energy saving methods of each species.

Predators generally have a high metabolism and will compensate by taking many rest periods. The same applies to small rodents with very high metabolic rates and high energy diets. Animals with a low metabolism can maintain low level activity most of the day. Elephant can plod along all day, with occasional rest periods, as they munch their way through a diet carefully chosen for its nutritional value. They may appear to have an inefficient digestion system but it is designed to produce meals for other animals, as do the elephant's tree breaking activities.

Baboons and monkeys may also appear to have inefficient and wasteful feeding methods but in natural areas they are dropping food for ground animals that are otherwise unable to reach the food source. Slow growing, hardwood trees, take in the sun's energy for longer and are thus are able to release more energy when burnt. They are, however, valuable nest sites and perches for some of our large birds, as I have previously mentioned, and should be left standing. Fast growing trees produce softer wood and take in less energy so don't burn as well as hardwoods.

Softwoods are attractive to wood borers, wood peckers and barbets and have an important role to play. As standing trees they provide protection for upper decomposers from the ravages of ants. All these decomposers provide a rich food source for many other animals. The decomposition processes are designed to return nutrients to the soil.

Most human activities disrupt or prevent these processes. Many trees have unpalatable leaves which deter browsers while other species are attractive and heavily browsed. Many of these palatable species produce deterrents such as tannins, hedging or thorns to protect them from overbrowsing. Because of these deterrents, browsers confined to small areas may starve despite the foliage apparently available to them. The visual assessment of 'available food' is not always a reliable guide to the quantity of 'palatable food'.

Food preferences must be taken into consideration. While on this aspect, animals moved from highveld to lowveld and vice versa will normally not be able to digest the food in the new area. Their digestive systems containing the wrong 'ruminal flora' (bacteria) and they need an introduction of local stomach bacteria. This would appear to be one of the reasons for animals defecating in water sources - to pass on valuable bacteria.

Early farmers knew to dose all new stock with the ruminal contents of a local animal before releasing them on the veld. Animals without the correct ruminal flora will starve to death with full stomachs. Getting back to the subject of energy saving. It becomes obvious why poorer nations are unable to produce or consume much meat.

The energy wastage in the conversion from grass or grain to meat is too high. You can have 100 kg of grain or only one kilogram of meat. In commercial agriculture, consider the 'clumping' and 'dividing' processes involved in bringing a wheat crop to your table. It is produced in a 'head'. It is reaped into separated grains. It is clumped into a bag. It is transported. It is poured into a mill and ground into particles of flour. It is then clumped into a small bag. Sold. Scattered into a bowl.

Clumped again into a lump of dough. Baked. Sold again. Sliced into pieces and then chewed into a pulp before being swallowed and finally digested. It could have been pulled off the head and placed straight into the mouth and chewed, saving a lot of energy. Of course it is not that simple in our distribution and manufacturing economies.

With each energy wasting process jobs are created and food made available to many other areas. It does start you thinking though, of the waste of energy and the increased cost of production caused by each 'change from one form to another'. The same applies to the manufacturing industry with the cost involved in each process.

In a world so starved of energy resources, be it food or power, it might be wise for industrialists, financial planners and those in government to spend more time quietly observing natural systems. There is no better teacher than unspoilt wilderness where there is no greed and where natural systems operate on sustainable incentives and profit margins.